Hello all, First post. I have a komatsu pc40 that I bought used about one year ago. It appears to have had a thumb on it at one time. I would like to put one on it now so i started today... Had the hydraulic lines made, had couplings, laser cut and welded the thumb, had a few cylinders- all set. Took the caps off the lines on the dipper and installed the couplings, threaded to the cylinder and decided to test the cylinder functionality before going any further. The cylinder only operated correctly one way (I switched the lines and the same side worked each time). So I am left with a cylinder that either goes up or down based on which side I plug in. Followed the lines back to the spool valve (foot control between). The cable that pulls on the valve (controlled by foot) wasn't allowing enough travel but that I can figure out. At this point I disconnected the cable and moved the valve in and out by hand. When I move the valve the direction that the cylinder doesn't want to go it bogs down the engine (sounding like the oil has no where to go) move it the other way and its fine (although I have to switch the lines again to retract or extend again). Tried another cylinder and got the same result so I must be missing something on the excavator. I did notice a hydraulic line that looked like a "loop" going to both the left and right side. I took it off and capped thinking that maybe the pressure was working against itself... No difference... Any ideas what I could be missing? Thank you! Brian
IT IS A SINGLE ACTING valve. DONT MOVE IT THE OTHER WAY. SOUNDS LIKE THERE IS NO RELIEF. THINGS WILL GET EXPENSIVE VERY FAST. You can set it up with one of these. This will be the fastest and least expnsive option http://www.surpluscenter.com/item.asp?item=9-7989&catname=hydraulic
so in order for the cylinder to move you must be providing pressure to one side and just as important return to tank on the other, so that being said this IS happening! my guess is there is a three way ball valve in that RETURN line that is directed to return oil directly to tank aka hammer or packer mode, when this valve is turned this direction it will block the pressure from the spool valve which would normally direct the cylinder the other direction (hence the dead heading pump noise), trace lines back until you find valve and turn it 90 degrees, problem solved>>>>>theironoracle, the loop hose probably has a valve on each end or on one end in line, this is a cross over relief valve, which means as you curl the bucket into the thumb the at a set pressure the oil will flow from one side of the thumb cylinder to the other in theory allowing the cylinder to collapse (enough discussion for another post can't deal with that here)!<<<<<<<<<TIO
Thank you guys for responding! From mikebramel and TIO's posts it sounds like the "loop line" needs to stay on. There are two valves (I thought they were shut off valves) just behind the couplings on the dipper, one on each side that turn 90 degrees. TIO, you were right there is what looks like a TEE at the loop line connections. I will take some pics quick so if I am describing it wrong you can correct me Also, if you would like to just call me, my # is 517-917-8952. May be easier to explain. I can also Skype- Brian_706. B
Mike, I checked out that valve and solenoid. Looks super cool in that it would make the thumb work electrically (like three way toggle) instead of via linkage. Am I reading that right?
I bleieve you have read correct. However my thinking is a resivor is necessay. There is a difference in volume of fluid needed to operate in extension vs retraction.
Post #4: Pic 1 - those are shut off valves. Pic 2 and 3 - that's a relief valve on the pressure line for a breaker that dumps oil back to the return line Pic 4 - main control valve. I can't say for certain because pic doesn't show enough detail, but it looks like only one of the aux lines is connected to the control valve. You need to follow both of the boom lines back to their source. From what you're describing, as stated previously, your system is single acting, one of those boom lines is going back to tank instead of to the main control valve.
first pic is a on/off two way ball valve, second is the cross over relief it needs connected to the large (barrel) end of the cylinder and loop hose reconnected, so lastly things were unfortunately not plumbed the way I assumed! that spool valve there in the middle should have two hoses (extend and retract) connected to it but it doesn't. so if that spool moved far enough to dead head the pump and there is a plug in that orifice I would assume it actually is a double acting spool (but I have been wrong before) at this point I would try to determine this, I do see there is no relief valve there and I would recommend installing one because I am not sure the cross over on the boom works both directions. as far as that solenoid operated valve I think it is at least one size to small, next problem is if that cross over relief doesn't work both ways you will bend something if your not careful because the spool returns to center which closes off all oil flow (no relief to tank) which allows no cylinder movement if you were to put pressure on the back side of the thumb. I prefer to keep things as stock as possible so adding valves rather than using what you got is not first choice for me, I prefer the electrical switches on the joy sticks but it only takes about 3 hrs to get used to using your foot to control the thumb..........that is it for now.....................TIO
that's hilarious same post same time just Willies is much easier to understand, maybe when I get to 8500+ posts I will be easier to understand! .............TIO
LoL...I think you just didn't notice me typing on the other side of the machine.
All great info- thank you guys! I will look at the line that doesn't seem to work (assuming that is the return line. That makes sense because the oil has to go somewhere when the cylinder moves). Single acting is probably right... That would be great for an auger but not for the thumb. The valve does look like there is a plug in one of the ports so maybe it is two way and they were just using it one way.. If I ran another line off that port (that is currently plugged) to the current dump line back to tank on the cylinder, then how would I incorporate the existing dump line (if I have one going to extend and one going to retract on the cylinder)? Also TIO, is the relief valve you are talking about just an add on to my existing valve? Thanks guys! B Pic 3 - the line was connected to right most port (the directional arrow is pointing to it)
Here is schematic of my control valve Line "C" is my service spool and the only line connected is on port B7 Here is another pic. B-B is the service spool. From everything I can see the valve should be able to be bi-directional with the right hoses connected to the right ports...extend cylinder, retract cylinder, pressure port and tank port. With only one hose connected it would only be uni-directional, right? Furthermore, does it appear that lines C,E, and D all use the same pressure port (Pc) and tank port (T) on first pic? Section C-C is the service spool that shows the four ports
Yes, that aux section (service spool) is like the other sections, it's a 4 way control valve, bi-directional as you called it. You need to connect your boom pipe hose to port A7. But one thing you are going to have to do to use the hyd thumb is obtain the two relief valves for the spool section. Without the relief cartridges you'll damage or destroy the cylinder on the thumb. And yes, all those spool sections use oil supplied by port Pr and return oil to tank via T port. If you get this rigged up with the proper relief cartridges, you won't be using the relief valve fitted at the boom piping, that relief valve will only work with a single acting circuit.